Swift Make For Loop wait for Asynchronous function to end - ios

Question

im trying to work with firebase, i made this function that is saving "Offers" to an Array and then sending this array to another viewcontroller to show them on a tableView.
i found a problem that the for loop is ending before the data is coming from the servers and the callback of firebase is coming, where u can see the line "fir (self.goodOffer...)" is the end of the firebase callback.
maybe someone know how can i make the for loop to wait for the firebase callback to end?
thx.
geocodeAddress(totalFromLocation, callback: { (location) in
if location != nil {
fromLocation = location
self.geocodeAddress(totalToLocation, callback: { (location) in
if location != nil {
toLocation = location
mainDistance = Int(self.distanceCalculate(fromLocation!, locationTwo: toLocation!))
print(mainDistance)
REF_BUSSINES_OFFERS.queryOrderedByKey().queryEqualToValue("north").observeSingleEventOfType(.Value, withBlock: { (snapshot) in
print("in snap")
if let value = snapshot.value {
if self.isAlavator {
if let area = value["north"] {
if let data = area!["withAlavator"]! {
if let bids = data["bids"] as? Int {
for i in 1..<bids+1 {
if let bid = data["\(i)"] {
let bidFromSize = bid!["fromSize"] as! Int
let bidToSize = bid!["toSize"] as! Int
let bidFromDistance = bid!["fromDistance"] as! Int
let bidToDistance = bid!["toDistance"] as! Int
if mainDistance >= bidFromDistance && mainDistance <= bidToDistance {
if Int(totalSize) >= bidFromSize && Int(totalSize) <= bidToSize {
let price = String(bid!["price"])
let name = bid!["name"] as! String
let phoneNumber = bid!["phoneNumber"] as! String
var logoImageData: NSData!
LOGOS_REF.child("\(phoneNumber)").dataWithMaxSize(3 * 1024 * 1024, completion: { (data, error) in
if error != nil {
logoImageData = UIImagePNGRepresentation(UIImage(named: "company")!)
} else {
logoImageData = data
}
let offer = Offer(logoImage: logoImageData, name: name, price: price)
self.goodOffers.append(offer)
print("fir \(self.goodOffers[0].price)")
})
}
}
}
print(i)
}//end of for
print("out")
//self.changgeViewToTable()
}

Answer 1

Can't help you much because your code is such a pain to read. Use ObjectMapper to reduce the level (and the effort) to map these fields. Anyhow, you can use dispatch_group to synchronize the various async calls:
let group = dispatch_group_create()
for i in 1..<bids+1 {
// ...
dispatch_group_enter(group)
LOGOS_REF.child("\(phoneNumber)").dataWithMaxSize(3 * 1024 * 1024) {
// ...
dispatch_group_leave(group)
}
}
// Wait for all async calls to complete before proceeding
dispatch_group_wait(group, DISPATCH_TIME_FOREVER)
Each dispatch_group_enter() should be balanced with a dispatch_group_leave() when the async task is complete.